Postharvest treatments against western flower thrips (Frankliniella occidentalis (Pergande)) and melon thrips (Thrips palmi Karny) on orchids.
Postharvest treatments, including insecticidal dips, isopropyl alcohol dips, insecticidal fogs and hot-water immersion, were evaluated to control mixed infestations of Frankliniella occidentalis and Thrips palmi on Dendrobium orchid blossoms. The limiting factor for all postharvest treatments was phytotoxicity, characterized by a loss of vase life that differed among cultivars. Insecticidal dips and insecticidal fogs were less phytotoxic than hot-water immersion and isopropyl alcohol dips. Insecticidal fogs consisting of abamectin 20% e.c. and abamectin tank-mixed with Pyrenone e.c. (6% pyrethrins, 60% piperonyl butoxide) reduced the mean number of thrips per blossom by 93.8 and 92.3%, resp., and were non-phytotoxic. An insecticidal aerosol, Floragas (2% permethrin and 0.1% pyrethrum dissolved in high pressure liquified CO2) reduced thrips by 33-54% with no phytotoxicity. Insecticidal dips for 3 min with agitation reduced the mean number of thrips per blossom by 43.7-99.1%. Of the 12 insecticides and one surfactant tested, only chlorpyrifos 44.4% e.c., fluvalinate 22.3% d.f., and chlorpyrifos 50% d.f. were both effective and nonphytotoxic. Immersion in water at 49.5°C for 15 and 20 s reduced the mean number of thrips per blossom by 88.1% and 95.3%, resp. A 70% solution of isopropyl alcohol applied as a postharvest dip did not kill all thrips and was extremely phytotoxic to blossoms.